One example application is in internal combustion engine fuel delivery systems. Fuel delivery systems for internal combustion engines are configured to draw fuel from the fuel tank and deliver it to the engine and may include a fuel pump and fuel filter. A fuel pump may provide the elevated pressures required by fuel injection systems. A fuel filter is typically provided and often interposed between the fuel tank and fuel pump to remove contaminant materials that may be present in the fuel supply.
Internal combustion engines may be configured to operate on a variety of fuel types. Internal combustion engines may utilize fuel varieties that are substantially more viscous in cold weather conditions (for example, diesel fuel) than is the case for other fuels (for example, gasoline). To improve operation of these engines in cold temperatures and to reduce fuel viscosity it is useful to provide a means to controllably mix preheated fuel with unheated fuel in the fuel supply delivered to the fuel filter and ultimately to the engine.
There are known solutions in the art. For example, EP1302711 discloses a thermostatic valve for a fuel supply to a diesel engine. The valve includes a movable valve member slideable within a valve body chamber utilizing radial sealing of the valve member to the valve body. A shape memory alloy component is provided to actuate the valve member at a transformation temperature. Unfortunately, this valve assembly has a number of disadvantages. The thermostatic valve senses the fuel temperature flowing into the inlet port of the valve (i.e., return fuel from the engine). This design, as it senses and responds to only the much warmer fuel return temperature, therefore does not provide the necessary control of the diesel fuel supply temperature to the engine. Another limitation is in the design wherein the valve member utilizes radial sealing to the valve body. Radial sealing is disadvantageous as the radial sealing gives rise to the need for tight tolerances between the valve member and the valve chamber walls. Free movement of the valve member inside the valve body relies upon maintaining very clean wall conditions between the sealing surfaces of the sliding valve member and the valve body wall against which the valve member slides. We have found that similar designs have shown problems where the valve member will catch or hang-up on debris that may accumulate between the sliding surfaces, a condition aggravated by the relatively tight tolerances of radial sealing. On the other hand, reducing the outside diameter of the valve member in EP1302711 to reduce the chance that the valve will “stick” will necessarily result in internal leakage paths that interfere with the accurate operation of the valve.
Another reference, U.S. Pat. No. 5,746,170 discloses a thermostatic valve disposed in an oil filter mounting block including a shape memory alloy member configured to actuate the valve on rising temperature to reroute oil flow to an oil cooler.
While such solutions are serviceable for their disclosed uses, they are disadvantageous from a fuel system operation and total system cost point of view. Therefore a better solution for controlling fuel temperature that is realizable at a lower cost, provides better control of delivered fuel temperature and is more easily implemented is desirable.